In a progressive-power spectacle lens, information necessary to edge a lens and inspect the optical performance of the lens is often temporarily printed on the optical surface of an uncut lens (a finished lens before edging), or an optically finished surface including the progressive surface of a semifinished lens.
Examples of the information to be printed include position indication marks (to be generically referred to as reference position indicators hereinafter) such as a processing reference point (fitting point), horizontal reference line, vertical reference line, distance portion measurement position (distance portion measurement reference point), near portion measurement position (near portion measurement reference point), and prism measurement reference point, indication marks (to be simply referred to as lens right or left indication marks hereinafter) indicating whether spectacle lenses (to be also simply referred to as lenses hereinafter) are right or left lenses, and indication marks (to be referred to as lens identification indication marks hereinafter) for identifying lenses, such as the lens product name, manufacturer's name, and blank name. An indicator formed by one or a plurality of combinations of these information will be referred to as a layout mark hereinafter.
FIG. 16 is a view illustrating an example of a left-eye progressive-power lens using an uncut lens having a layout mark formed on it. As for a layout mark on a progressive-power lens 110, it is generally printed on the front surface of the lens with white ink. The layout mark in this example is formed by a combination of horizontal reference lines 112A and 112E which pass through two permanent alignment reference marks 111A and 111B, respectively, on the progressive-power lens 110, a distance portion measurement position indication mark 113 indicating the position of a distance portion measurement reference point, a near portion measurement position indication mark 114 indicating the position of a near portion measurement reference point, a dot 115 indicating the position of a prism measurement reference point, an indication line 116 indicating the height of a fitting point, a lens right or left indication mark 117, a lens identification indication mark 118, and vertical reference lines 119A and 119E which pass through the prism measurement reference point. Note that the position of the fitting point in this example can be determined based on the intersection between the vertical reference lines 119A and 119B and the fitting point height position indication line 116.
Such a layout mark normally becomes unnecessary after edging, and is therefore printed on a lens using ink that can easily be removed using an organic solvent such as an alcohol.
As a conventional method of printing such a layout mark, it is a common practice to prepare a plate for each layout mark in advance, transfer ink from the plate onto a stamp, and further transfer the ink from the stamp onto the optical surface of a lens. However, in recent years, printing techniques which can cope with various layout marks by changing the discharge pattern using an inkjet printer have been proposed (see, for example, patent literatures 1 and 2).
A marking method described in patent literature 1 discharges hot-melt ink, which is thermally melted based on a pattern generated by a pattern generation unit, from an inkjet head onto the surface of a lens as minute liquid droplets to print, for example, a predetermined pattern.
A marking method described in patent literature 2 includes a pattern generation process of generating a layout pattern based on an inset amount and corridor length given by designating arbitrary numerical values, and prints a layout pattern generated in the pattern generation process on the printing surface of a lens using an inkjet printer.